Full-profile Refinement Research Articles

Na2B6Si2: A Prototype Silico-boride with Closo (B6)2- Clusters.

The compound Na2B6Si2 was synthesized under high-pressure, high-temperature conditions at pressures ranging from 6 to 9.5 GPa and temperatures from 1070 to 1270 K before quenching to room temperature followed by slow decompression. The crystal structure was determined from microcrystals using precession-assisted electron diffraction tomography, validated by dynamical refinement and full-profile refinements using optimized coordinates from quantum chemical calculations (space group R3̅m, Pearson symbol hR30, a = 5.0735(1) Å and c = 16.0004(7) Å). The atomic arrangement consists of a unique framework formed by electron-precise octahedral closo (B6)2- clusters connected via ethane-like (Si2)0 dumbbells. The Na+ cations occupy cavities in the hierarchical variation of a Heusler-type framework. The balance (Na+)2([B6]2-)(Si0)2 reveals an electron precise Zintl-Wade phase, which is in line with electronic band structure calculations predicting semiconducting behavior.

Intermediate valence behavior of the ternary cerium-nickel-phosphide Ce2Ni12P5

The crystal structure of the ternary phosphide Ce2Ni12P5 (La2Ni12P5-type structure) has been determined from X-ray powder diffraction data: full profile refinement, monoclinic symmetry, space group P21/m, a = 10.7809(2) Å, b = 3.6869(1) Å, c = 13.1490(3) Å, β = 107.776(4)º, RI = 0.068, RP = 0.044, RwP = 0.060. Ce2Ni12P5 is a ferromagnet with a Curie temperature of 5.8(5) K. A significant deviation from the linearity of the temperature dependence of the electrical resistance for Ce2Ni12P5 has been found. The low-temperature part of the electrical resistance indicates the presence of magnetic interactions in Ce2Ni12P5. The influence of a magnetic field on the electrical resistance of Ce2Ni12P5 has been studied. The X-ray absorption spectrum at the Ce LIII edge and X-ray emission spectra of Ni and P at the K and LIII edges have been studied experimentally and theoretically using DFT+U calculations. The calculations show good agreement with the experimental measurements. The effective valence of Ce in Ce2Ni12P5 determined based on the Ce LIII absorption spectrum is ϑeff ∼ 3.05.

Principal Preferred Orientation Evaluation of Steel Materials Using Time-of-Flight Neutron Diffraction

Comprehensive information on in situ microstructural and crystallographic changes during the preparation/manufacturing processes of various materials is highly necessary to precisely control the microstructural morphology and the preferred orientation (or texture) characteristics for achieving an excellent strength–ductility–toughness balance in advanced engineering materials. In this study, in situ isothermal annealing experiments with cold-rolled 17Ni-0.2C (mass%) martensitic steel sheets were carried out by using the TAKUMI and ENGIN-X time-of-flight neutron diffractometers. The inverse pole figures based on full-profile refinement were extracted to roughly evaluate the preferred orientation features along three principal sample directions of the investigated steel sheets, using the General Structure Analysis System (GSAS) software with built-in generalized spherical harmonic functions. The consistent rolling direction (RD) inverse pole figures from TAKUMI and ENGIN-X confirmed that the time-of-flight neutron diffraction has high repeatability and statistical reliability, revealing that the principal preferred orientation evaluation of steel materials can be realized through 90° TD ➜ ND (transverse direction ➜ normal direction) rotation of the investigated specimen on the sample stage during two neutron diffraction experiments. Moreover, these RD, TD, and ND inverse pole figures before and after the in situ experiments were compared with the corresponding inverse pole figures recalculated from the MUSASI-L complete pole figure measurement and the HIPPO in situ microstructure evaluation, respectively. The similar orientation distribution characteristics suggested that the principal preferred orientation evaluation method can be applied to the in situ microstructural evolution of bulk orthorhombic materials and spatially resolved principal preferred orientation mappings of large engineering structure parts.

Influence of phase composition and crystal structure on the luminescent properties of calcium aluminates (CaAl2O4, CaAl4O7, CaAl12O19) activated by Eu3+ ions

Calcium monoaluminate, dialuminate, and hexaaluminate and luminophores based on them activated by europium (III) ions were obtained by the citrate-nitrate gel method. X-ray diffraction (XRD) and Full-Profile Rietveld refinement were used to establish the parameters of single-phase systems, to analyze the structure of the investigated compounds, and to determine the most probable sites of calcium substitution by the activator. The interpretation of the emission spectra has shown that europium occupies two crystallographic positions in calcium monoaluminate, while in dialuminate and hexaaluminate europium has only one crystallographic environment. Phosphor emission bands lie in the range from 580 to 720 nm, but the splitting of bands and their intensity are different. This is due to the different symmetry of the europium environment in the aluminate matrixes. This makes it possible to obtain phosphors of different hues of luminescence from the same starting materials, which is confirmed by the Commission Internationale de L'Eclairage (CIE) chromatic coordinate diagram.

Experimental investigation of the solid phase equilibria at 300 K in the SnBi2Te4-PbBi2Te4-Bi2Te3 system

The phase equilibria of the SnBi2Te4-PbBi2Te4-Bi2Te3 system were experimentally studied using differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques. According to the experimental results, the isothermal section of the system at 300 K were constructed and 4 single-phase and 3 two-phase regions were identified. It was shown that along with previously confirmed SnBi2Te4–PbBi2Te4 and SnBi4Te7–PbBi4Te7 sections, SnBi6Te10–PbBi6Te10 section forms continuous series of solid solutions with a tetradymite-type layered structure. Lattice parameters of solid solutions were determined by full-profile Rietveld refinements and results show that both a and c parameters increase linearly with the Pb concentration according to Vegard's law. This study can help elucidate the phase equilibria of the SnTe-PbTe-Bi2Te3 pseudo-ternary system which provides important information for the design of new tetradymite-type layered phases with topological insulator and thermoelectric properties.

Crystal Structure of Poly(7-heptalactone)

The crystal structure of poly(7-heptalactone) (PHL) is presented. PHL has been synthesized by a combination of ring-opening polymerization of η-heptalactone and reversible addition–fragmentation chain transfer polymerization using diphenyl phosphate as catalyst. The noncommercial available η-heptalactone monomer has been prepared by oxidation of cycloheptanone. The crystal structure of PHL has been determined by analysis of the X-ray powder diffraction profiles and of the electron diffraction patterns of single crystals and calculations of lattice energy. The structure has been refined with the Rietveld full-profile refinement. Chains in trans planar conformation are packed in an orthorhombic unit cell with axes a = 7.37 Å, b = 5.05 Å, and c = 10.07 Å according to the space group symmetry P21.

CRYSTALS GROWTH AND REFINEMENT OF THE Cu3SbSe3 CRYSTAL STRUCTURE

The technology of thermoelectric converters, based on the Peltier and Seebeck effects, provides a reversible process of convert in thermal and electrical energy. This opens up prospects for the creation of both thermoelectric coolers and thermoelectric generators. The most widely studied class of thermoelectric materials are complex chalcogenides. In recent years, copper-containing chalcogenides have been actively researched as new highly effective and ecologically friendly thermoelectric materials. The Cu–Sb–Se ternary system are characterized by the existence of three phases CuSbSe2, Cu3SbSe3 and Cu3SbSe4. Among these compounds, the Cu3SbSe3 phase is characterized by the lowest thermal conductivity.
 The synthesis of the Cu3SbSe3 polycrystalline alloy was carried out using high purity elementally components. The synthesis was carried out in vacuumed quartz ampoules by a one-temperature, two-stage process. Taking into account the incongruent melting of Cu3SbSe3, the single crystal growth was carried out by the method of vertical zone crystallization from a solution-melt in vacuumed conical quartz ampoules. As a result, the grown single crystal was dark gray color with metallic luster, without defects with length ~ 40 mm and diameter 12 mm.
 Obtained single crystalline sample of Cu3SbSe3 was investigated by DTA method. The heating curve contains one endothermic effect at 530°С, which corresponds to the process of peritectic decomposition of Cu3SbSe3. The effect corresponding to the melting of all components in the quartz container is not fixed. However, it is clearly visible on the cooling curve at 712 °С. The exothermic effect of crystallization of Cu3SbSe3 (503 °С) is clear and sharp and is observed with supercooling ΔТ = 27 °С. To confirm the single crystallinity of grown Cu3SbSe3 sample, an XRD analysis of the natural surface was carried out. The diffraction pattern shows two clear and narrow diffraction peaks corresponding to the (200) and (400) planes at angles of 22.27° and 45.42°, respectively. The crystal structure of the obtained Cu3SbSe3 single crystal was investigated by XRD analysis using the Rietveld full-profile refinement method. Established that Cu3SbSe3 crystallize in orthorhombic crystal system, SGPnma with lattice parameters: a = 7.9668 Å, b = 10.65870 Å, c = 6.8207 Å, Z = 4.

Role of rare earth sites and vacancies in the anomalous compression of modulated scheelite tungstates RE2 ( WO4)3

X-ray powder diffraction experiments at high pressures combining conventional sources and synchrotron radiation, together with theoretical simulations have allowed us to study the anomalous compression of the entire \ensuremath{\alpha}-${RE}_{2}$(${\mathrm{WO}}_{4}{)}_{3}$ ($\mathit{RE}$ = La-Ho) family with modulated scheelite structure (\ensuremath{\alpha} phase). The investigated class of materials is of great interest due to their peculiar structural behavior with temperature and pressure, which is highly sought after for specialized high-tech applications. Experimental data were analyzed using full-profile refinements and were complemented with computational methods based on density functional theory (DFT) total energy calculations for a subset of the samples investigated. An unusual change in the compression curves of the lattice parameters $a, c$, and \ensuremath{\beta} was observed in both the experiments and theoretical simulations. In particular, in all the studied compounds the lattice parameter $a$ decreased with pressure to a minimum value and then increased upon further compression. Pressure evolution of the experimental x-ray diffraction (XRD) patterns and cell parameters is correlated with the ionic radius of the rare earth element: (1) the lighter La-Nd tungstates underwent two phase transitions, and both transition pressures decreased as the rare earth's ionic radius increased. The XRD patterns of the first high pressure phase could be indexed with propagation vectors parallel to the $a$ axis (tripling the unit cell). At higher pressures, the lattice parameters for the second phase (referred to as the preamorphous phase) showed little variation with pressure. (2) The heavier tungstates, from Sm to Dy, undergo a transition to the preamorphous phase without any intermediate phase. The reversibility of both phase transitions was investigated. DFT calculations support this unusual response of the crystal structures under pressure and shed light on the structural mechanism of negative linear compressibility (NLC) and the resulting softening. The pressure dependence of the structural modifications is related to tilting, along with small elongation and alignment, of the ${\mathrm{WO}}_{4}^{2\ensuremath{-}}$ tetrahedrons. These changes correlate with those in the alternating RE\dots{}RE\dots{}RE chains and blocks of cationic vacancies arranged along the $a$ axis. Possible stacking defects, which emerge between them, helped to explain this anomalous compression and the pressure induced amorphization. Such mechanisms were compared with other ferroelastic families of molybdates, niobates, vanadates, and other compounds with similar structural motifs classified as having ``hinge frames.''

Heat Capacity and Thermodynamic Functions of Sr(La1-xLnx)2WO7 Compounds Doped with Samarium and Europium

Samples based on strontium, lanthanum and tungsten with the general formula of Sr(La1-xLnx)2WO7 doped with samarium and europium at 1 and 3 at.% were synthesized by the solid-phase method at temperatures up to 1200 °C. The crystal structure of the samples was confirmed by X-ray powder diffraction. A full-profile refinement of the structure of compounds related to monoclinic syngony with the space group P1121/b was performed. The admixture phase is a compound of the Sr3Ln2W2O12 type with a trigonal system and space group R3-C. Based on the results of structure refinement, the ratio of the main compound and the admixture phase in the samples was determined to introduce corrections during measurements. Using adiabatic calorimetry we measured the heat capacity of the samples and found the thermodynamic functions of main compounds over the range of 5‒320 K. Anomalies were detected in the heat capacity of the samples below 15 K, and we calculated the excess and lattice heat capacity for these anomalies by means of linearization methods.

Structural, surface and optical properties of nanoalumina produced by various ways

Start The compared study of the properties of liquid-phase and electric explosion alumina nanoparticles was made. The X-ray diffraction analysis demonstrated that these nanoparticles remain in amorphous and semi-amorphous states. The complete structural information of Al2O3 nanoparticles was obtained as a result of the full-profile refinement of their model phase parameters. The parameters of the unit cells, spatial distribution of atoms, and occupancy of nodes were also determined.The data of IR spectra of surface OH groups and adsorbed CO revealed that the surface imperfection of an electric explosive sample is lower than that obtained using the liquid-phase method. Using photoluminescent spectroscopy, impurities of Cr3+, Mn4+ and Ti3+ in the octahedral oxygen coordination and Fe3+ in the tetrahedral oxygen coordination were detected. It was observed that the concentration of these impurities was significantly higher in the electric explosion sample. Using UV-Vis DR spectroscopy, it was found that the liquid-phase sample was amorphous, and the electric explosive sample was well crystallized and most probably consisted of 2D and 3D nanostructures.

Structural Characteristics and Thermodynamic Functions of Compounds Ba(La1–xPrx)2WO7 (x from 0.005 to 0.05)

A sol–gel method was used to synthesize barium, lanthanum, and tungsten-based samples doped with praseodymium Ba(La1–xPrx)2WO7, where x = 0.005 ÷ 0.05. The morphological and elemental analyses of the samples were carried out by electron probe microanalysis. A full-profile refinement of the crystal structure of the compounds belonging to the monoclinic system with the space group P1121/b was carried out. Using the adiabatic calorimetry method, the heat capacity of the samples was measured and the thermodynamic functions in the range of 5–320 K were found. In the heat capacity of the samples below 15 K, anomalies were detected and the excessive and lattice heat capacities were determined.

A New Kaolin Deposit in Western Africa: Mineralogical and Compositional Features of Kaolinite from Caluquembe (Angola)

AbstractLarge kaolin deposits developed by weathering on Precambrian granitic rocks have been discovered in the Caluquembe area, Huíla province, Angola. To determine accuracy of analysis and to evaluate the kaolinite grade, a full-profile Rietveld refinement by X-ray Powder Diffraction (XRPD) and Thermal Gravimetric Analysis (TGA) was used. Caluquembe kaolin is composed mainly of kaolinite (44–93 wt.%), quartz (0–23 wt.%), and feldspar (4–14 wt.%). The Aparicio-Galán-Ferrell index (AGFI), calculated by XRPD profile refinement, indicates low- and medium-defect kaolinite. Kaolinite particles show a platy habit and they stack together forming ‘booklets’ or radial aggregates; they also occur as small anhedral particles in a finer-grained mass. Muscovite-kaolinite intergrowths have also been found. Whole-rock chemical analysis included major, trace, and Rare Earth Elements (REE). Chondrite-normalized REE patterns show the same tendency for all samples, with a significant enrichment in Light Rare Earth Elements (LREE). Mineralogical and compositional features of the Caluquembe kaolin indicate that it is a suitable material for the manufacture of structural products, such as bricks, paving stones, and roofing tiles. In addition, the significant REE contents of the Caluquembe kaolin can be considered as a potential future target of mining exploration.

The Effects of La Doping on the Crystal Structure, Magnetic, and Microwave Absorption Properties of Nd2Fe14B Compound

The crystal structure, magnetic, and microwave absorption properties of the (Nd1−xLax)2Fe14B system have been investigated. The La2Fe14B compound was successfully synthesized and refined, giving a tetragonal structure, space group P42/mnm with the Nd2Fe14B-type structure. The crystal structure parameters of the (Nd1−xLax)2Fe14B compounds were determined by full-profile Rietveld refinements. The results revealed that all intermediate alloys form a continuous solid solution. The normalized lattice parameters of the (Nd1−xLax)2Fe14B compounds increase linearly with an increase of La concentration. Based on the results of DSC measurements and X-ray powder diffraction examinations, the phase diagram of the Nd2Fe14B-La2Fe14B system has been constructed. The remanence (Mr) and coercivity (Hc) of (Nd1−xLax)2Fe14B (x = 0.00, 0.10, 0.20, 0.30, and 0.40) gradually decrease. The highest reflection loss is − 29.8, − 27.4, − 24.1, − 18.6, and − 14.2 dB at 9.8, 8.9, 7.5, 6.9, and 6.5 GHz, respectively. The absorption peak shifts toward from higher frequency region to lower frequency region and the absorption bandwidth widens with the increase of the La substitution.

Improved electrochemical performances of LiMnPO4 synthesized by a hydrothermal method for Li-ion supercapatteries

Developing high-performance positrode materials are essential to attain high energy supercapatteries. In this regard, the electrochemical performances of the hydrothermally synthesized LiMnPO4 are studied. The crystal structures of the materials are elucidated using Full-profile XRD Rietveld refinement. The LiMnPO4 particles showed uniform elongated spherical shape with rice-like morphology. The rice-like LiMnPO4 showed a higher specific capacity of 492 C g−1 at 2 mV s−1 than highly agglomerated particles synthesized through sol–gel thermolysis method (191 C g−1) in 1 M LiOH aqueous electrolyte. The supercapattery is fabricated with rice-like LiMnPO4 and activated carbon (AC) as positrode and negatrode, respectively. The supercapattery (AC||LMP-H) delivered a higher capacitance around 99 F g−1 along with an improved energy density of 31 Wh kg−1. On the other hand, the LiMnPO4 prepared by sol–gel thermolysis method exhibited a very low capacitance of 35 F g−1 at 0.6 mA for the fabricated device (AC||LMP-S) with the lesser energy density about 11 Wh Kg−1 at a power density of 198 W kg−1. The reason behind the improved performance is explained based on the crystal structure as well as lower charge transfer resistance.

Simulation of the structural state of amorphous phases in nanoscale SiO2 synthesized via different methods

The structural state in nanoscaled SiO2 is probed experimentally via X-ray diffraction and the simulation method. The aerosil nanoparticles and nanoparticles synthesized via the electron beam evaporation are compared. The nanoparticles for all samples are shown to be in the amorphous state. The amorphous state of a SiO2 unit lattice is simulated via the molecular dynamics. The full-profile refinement of parameters for a simulated SiO2 phase (the Rietveld method) has allowed the complete structural information to be established at varying the specific surface. The unit cell parameters, the spatial atomic distribution and the degree of cell node occupation are determined, as well. The specific surface area is shown to decrease in aerosil nanoparticles and to increase in tarkosil nanoparticles with the increasing binding energy of atoms in a cell.

Modeling of the Structural State of Amorphous Phases of the Nano-Sized Al2O3 Produced by Different Synthesis Methods

The paper examines the structural state of the Al2O3 alloy nanopowders synthesized by different methods: electron beam evaporation, hydrolysis, and plasma-chemical method. X-ray structural analysis demonstrated that Al2O3 nanopowders synthesized by different methods are in X-ray amorphous and semi-amorphous states. These synthesis methods stimulate the creation of amorphous structures with different specific surfaces. The structural state of the Al2O3 alloy was studied by methods of X-ray structural analysis and simulation modeling. In order to identify the internal structure, modeling of the amorphous state of the elementary cell of the Al2O3 phase was performed within molecular dynamics. As a result of full-profile refinement of parameters of the model phases of Al2O3 nanopowders, complete structural information was identified for the synthesized Al2O3 alloys. It was shown from first principles that the cells of X-ray amorphous Al2O3 turned out to be highly stable. Researchers identified the parameters of elementary cells, spatial distribution of atoms, and node occupancy. It was shown that specific surface increases in the Al2O3 alloy nanopowders with the increase in bond energy of atoms in the cell.

XRD study of phase transformations in lithiated graphite anodes by Rietveld method

Commercial anodes with different state of charge are investigated by X-ray diffraction technique using Rietveld method for data collected with standard laboratory equipment. It is shown that full profile refinement gives good approximation for quantitative description of the charge/discharge process and may be used for estimation of real state of charge (SoC). Careful analysis of the diffraction profile with Rietveld method allows us to quantitatively distinguish the contribution of different LixC6 phases and estimate the real SoC.

Novel route to synthesize metallic alloys by applying low energy centrifugal field

The aim of this work is to study the influence of a low energy centrifugal field in the solid solution formation of two binary systems: Cu–Cr and Cu–Ni. Pristine metal powders were milled separately in shaker mill during 8 h. Subsequently, disc‐shaped samples of Cu–50 wt.%Cr and Cu–50 wt.%Ni were prepared blending 0.5 g of each metallic powder and compacting them by applying a pressure of 25 MPa. The discs were introduced in sample holders of 150 mm of length, to subject the samples to a centrifugal field with and without temperature treatment. Powder X‐ray diffraction analysis was used to determine the lattice parameters and crystallite size changes of both systems. The lattice parameters of fcc Cu–Cr and fcc Cu–Ni solid solutions were computed using ab initio methods. XRD full profile refinements were performed by means of the Rietveld method using the software MAUD. The lattice parameters of Cu, Cr, and Ni changed in the samples subjected to the action of the centrifugal field applied, showing that the centrifugal field influences the formation of solid solution in the Cu–Cr and Cu–Ni systems. Experimental and thermodynamic data support the formation of solid solutions by subjecting the metal powders to the action of a centrifugal field.

X-ray and dielectric characterization of Co doped tetragonal BaTiO3 ceramics

ABSTRACTThe crystal structure modifications of BaTiO3 induced by cobalt doping were studied. The polycrystalline (1 − x)BaTiO3 + xCo2O3 samples, with x ≤ 10 wt.%, were prepared by high temperature sintering conventional method. According to X-ray phase and structural characterization, performed by full-profile Rietveld refinement technique, all synthesized samples showed tetragonal symmetry perovskite structure with minor amount of parasitic phases. Pure single-phase composition has been detected only in the low level of doping BaTiO3. It was indicated that substitution of Co for the Ti sites in the (1 − x)BaTiO3 + xCo2O3 series led to decrease of tetragonality (c/a) of the BaTiO3 perovskite structure. This effect almost vanished in the (1 − x)BaTiO3 + xCo2O3 samples with nominal Co content higher than ∼1 wt.%, in which precipitation of parasitic Co-containing phases CoO and Co2TiO4 has been observed. Based on the results, the solubility limit of Co in Ti sub-lattice in the (1 − x)BaTiO3 + xCo2O3 series is estimated as x = 0.75 wt.%.

Crystal structure and phase relations of Pr2Fe14B-La2Fe14B system

The crystal structure and phase relations of the Pr2Fe14B-La2Fe14B system were investigated by X-ray powder diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). The crystal structure parameters were determined by full-profile Rietveld refinements. The results revealed that all alloys of (Pr1–xLax)2Fe14B crystallized the Nd2Fe14B-type structure with the space group P42/mnm and formed a continuous solid solutions between x=0.0 and 1.0. The lattice parameter a, c, unit-cell volume V and c/a ratio increased linearly with the La concentration. Determined by thermogravimetry analysis, the Curie temperature (TC), phase transition temperature and melting temperature of (Pr1–xLax)2Fe14B decreased linearly upon the La content. Based on the results of DSC measurements and X-ray powder diffraction examinations, the phase diagram of the Pr2Fe14B-La2Fe14B system was built up.